1. Field of the Invention
This invention relates generally to process challenge devices, in particular to process challenge devices, using biological indicator organisms sealed in containers made from specially chosen materials, used to assess the efficacy of procedures for the inactivation of microorganisms in industries related to health care, food packaging and preparation, and other industries that use biological indicators.
2. Description of the Prior Art
Presently, there are two conventional methods to test the effectiveness of a given sterilization, disinfection, or biological inactivation process (hereafter referred to collectively as "inactivation process"). The first is to inoculate a sample product with a known quantity of a specific indicator organism (the "inoculate"), subject the inoculated product to the appropriate process, recover the sample inoculate, and culture the inoculate in a specific growth medium to determine whether there were any surviving organisms. The second is to use a biological indicator which is inoculated with a known quantity of a specific indicator organism, subject the biological indicator to the appropriate process, and culture the biological indicator to determine whether there are any surviving organisms. Typically, in both cases the absence of growth of the indicator organisms in the growth medium indicates a successful inactivation process. Direct inoculation of sample product is generally done during early validation of a biological inactivation process. Biological indicators are generally used to test repeat processing.
Currently there are three primary inactivation processes employed in the health care industry: steam, ethylene oxide gas, and ionizing radiation. Several other processes such as dry heat, hydrogen peroxide, chlorine dioxide, peracetic acid, ozone, and plasma are also in various stages of use and acceptance.
Each of these inactivation processes require unique biological indicator organisms, growth media, and procedures to confirm sterilization effectiveness. Among the problems associated with confirming biological inactivation and thus the effectiveness of process are: (a) the lack of commercial availability of appropriate carrier media for some of the newer processes; (b) the difficulty in inoculating products to be tested due to product/package configuration; (c) the cost of using actual products that must be sacrificed for the initial process qualification and the lot-to-lot verification of the process in every process test cycle; and (d) concerns regarding worker exposure to certain of the chemical sterilants, (for example, the European Standard for ethylene oxide processing requires removal of the biological samples prior to degassing the product).
Self-contained process challenge devices containing biological indicator organisms which do not require inoculation of a product are in use in health care facilities such as hospitals. The resistance of a process challenge device to a particular biological inactivation process is given as a D Value which is defined as the exposure time required under a defined set of conditions to cause a 1-logorithm or 90% reduction in the population of a particular organism. Process challenge devices currently on the market have a single unchanging D Value. In order to create the higher resistance to the inactivation process experienced by actual product being processed, due to packaging of the product, the location of a product within a load being processed, or other factors, these devices must generally be wrapped or contained within packaging or other protective material similar to that used on the products being sterilized, so that the process challenge device is exposed to the same environment as the products being processed. Altemativley, in some cases the process challenge device is buried in the most protected location within a load being sterilized. Therefore, these devices cannot be used alone to validate a biological inactivation process without additional protection from the process to simulate the higher resistance of the actual products to the process.
For example, Welsh et al., U.S. Pat. No. 4,839,291, discloses a process challenge device which is composed of a number of elements including an outer tube and an inner tube assembled in a manner intended to create a tortuous path to impede the flow of sterilant to the biological indicator contained within the tubes, thereby creating a D Value. Typical of many prior art devices, the device of Welsh et al. is larger and more expensive to manufacture than the present invention, and its resistance to a particular sterilization process may not be easily and accurately varied merely by using slightly different materials in construction of the device. Additionally, the materials used may not be suitable for the newer inactivation processes, such as hydrogen peroxide, ozone, and plasma, because the sterilants used may destructively react with elements of the process challenge device.
It would be a significant advantage to provide a process challenge device which overcomes the disadvantages of the prior art devices, and which can, in addition, be constructed with resistance tailored to a particular biological inactivation process to avoid the need for destructive testing of product, the need for additional packaging of or protective covering over the process challenge device, or the necessity of placing one or more devices within an actual load.